1. Field of the Invention
This invention is related generally to aerosol traps, and, more particularly, to methods and apparatus for collecting aerosols in exhaled breath in a reliable and reproducible manner for diagnostic and other purposes.
2. State of the Prior Art
Exhaled breath comprises gaseous materials, such as carbon dioxide, oxygen, water vapor, and others, and non-gaseous materials, such as liquid droplets, insoluble substances, and mixtures of the two. Materials in the exhaled breath that are not in the gaseous state at the opening of the mouth or nose when exhaled are considered to be aerosols for the purposes of this discussion. Some examples of such aerosols may include airborne solid particulates, such as dust and smoke, as well as liquid droplets that comprise drugs, biological materials, and other chemicals that can be subjected to analysis, i.e., analytes.
Most standard clinical analytes, i.e., substances that are the subjects of analyses, are not volatile, thus do not evaporate, at normal physiological (body) temperatures. Nevertheless, research investigators have observed such non-volatile components as drugs, proteins, electrolytes, and other analytes in condensates from exhaled breath. In 1987, Fairchild et al., “Particle Concentration in Exhaled Breath,” Am. Ind. Hyg. Assoc. J., Vol. 48, 1987, pp. 948-949, demonstrated that exhaled breath contains very finely divided and very sparse aerosols of suspended materials, with the smallest particles being smaller than 100 nanometers. Some research investigators presume, therefore, that non-gaseous materials recoverable from exhaled breath are transported in the breath by means of such aerosols in the breath.
There are numerous reports of studies in which such non-gaseous constituents (analytes) of exhaled breath have been collected along with water condensate from the breath in cold-surface condensers. In cold-surface condenser processes, exhaled breath from deep in the lungs is saturated with water vapor. Air within the upper airway of the body is slightly less humid, but it does gain some humidity over ambient air from the surrounding tissues in the airway between the lungs and lips. Thus, exhaled breath, which is a mixture of such saturated air from deep in the lungs along with such slightly less humid air in the upper airway, is quite humid. When such humid, exhaled air is directed against a cold surface, for example, a cold surface in a cold-surface condenser, the water vapor in the exhaled air condenses to liquid water, and it has been noted that the condensed water dissolves some of the non-volatile, aerosol constituents (analytes) from exhaled air that happen to come into contact with the condensed water. Unfortunately, however, such inclusion of non-volatile constituents in solution with the condensate occurs only if the non-volatile constituents happen to contact the condensation and is too inconsistent to be used for reliable, reproducible, and comparable non-volatile analyte collections.
Some non-gaseous substances in the exhaled breath are capable of indicating one or more physiological conditions of a person or animal, thus may be analytes with potential for diagnostic and other research and clinical purposes. For example, exhaled air contains some blood-borne substances and may be rich in markers that are useful in diagnosis of lung or airway diseases. One particularly interesting marker in exhaled breath, adenosine, may have the potential of indicating whether a person suffers from oxygen shortage to heart muscle (cardiac ischemia), which, if unresolved, may lead to the death of heart muscle cells, i.e., heart attack.
Unfortunately, however, measurements of aerosol analytes in exhaled breath captured by condensation and other methods prior to this invention have shown excessively high variance from one measurement to the next and have been very inconsistent. Therefore, they have not been reliable or useful for detecting or discriminating one pathological or physiological state from another. Some causes of such extreme variances in, for example, surface and other condenser methods may include: (i) Collector efficiency variations from one collection apparatus to another and even from one collection event to another with the same apparatus; (ii) The volume and flow rate of exhaled breaths may be highly variable from one person to another and even from the same person from one breath to another, thus presenting the collector apparatus with an irreproducible flow of breath material from which to collect samples; (iii) Surface condensation captures aerosol analytes only indirectly, thus previous state-of-the-art collectors may capture only non-predictable and non-verifiable portions of the aerosol analytes in the exhaled breath; (iv) Condensation may cause very high dilution of dissolved analytes, thereby leading to large and irregular losses.